Vinyl chloride resin with lead salt and hindered phenol stabilizers



VINYL CHLORIDE RESIN WITH LEAD SALT AND HINDERED PHENOL STABILIZERSClayton S. Myers, Fanwood, Joseph E. Wilson, New Brunswick, and RobertBostwick, Somerville, N. L, assignors to Union Carbide Corporation, acorporation of New York No Drawing. Continuation of application SerialNo. 261,573, December 13, 1951. This application March 17, 1954, SerialNo. 416,946

4 Claims. (Cl. 260-4555) Plastic compositions based on polymers orcopolymers of vinyl chloride are well established industrial products.The successful utilization of these materials has required the art todevelop means to inhibit or delay the blackening or degradation of thevinyl chloride resins which occurs on heating. The more seriousdegradation of the polyiner on severe heating is a partial chemicaldecomposition caused by the splitting out of hydrogen chloride fromnited States atent-O the molecule. There are a number of stabilizers inuse I which are capableof delaying or retarding this chemicaldecomposition, and many of such stabilizers are basic in character andserve to neutralize the released acid. However, in addition to thisprimary decomposition, a secondary degradation caused by oxidation orheat may occur which can result in the development of color or odor inthe plastic composition, impairment of its strength, elasticity orelectrical insulating capacity, or undesirable processingcharacteristics, such as sticking to the calender rolls or poorheat-sealing properties. The instability of other ingredients of thecomposition, such as plasticizers, lubricants and dyes, is also acontributing factor to this secondary decomposition.

Some of the better primary stabilizers will also inhibit the secondarytype of decomposition, but none are completely satisfactory in thisrespect particularly with regard to eliminating odors or preventing thedevelopment of an initial color on milling the composition to flux theresin and plasticizer. We have discovered a class of auxiliarystabilizers which, when added to a vinyl chloride resin compositioncontaining a primary stabilizer, Will greatly retard the development ofcolor and odor on heating the composition. These auxiliary stabilizersare hindered phenols in which all positions ortho or para to a hydroxylgroup are substituted by hydrocarbon radicals.

While phenols have been proposed as primary or secondary stabilizers,none of those heretofore suggested have been successful because of theirown inherent instability leading to their oxidation to severely coloredproducts. Thus, the addition of such phenols to vinyl chloride resinscontributes to the very condition they are designed to correct. Typicalof the phenols suggested in the art are phenol, o-phenyl-phenol ando-cresol. On the other hand, the hindered phenols of this inventionwhich are completely substituted in the ortho and para positions do notdiscolor on heating under the conditions used in this invention, andtherefore they are valuable auxiliary stabilizers for the vinyl chlorideresins.

The hindered phenols of this invention may be classed in two groups. Onegroup comprises the 2,4,6-trialkyl substituted phenols of the formula:

2 where R R and R are alkyl groups. Preferably the radicals R and R inthe 2 and 6 positions are tertiary alkyl groups whereas the radical Rmay be alkyl'or tertiary alkyl. The other group includes 2,2-methylene'bis-4-6-dialkyl phenols of the formula: I

OH OH Rr- R:

I i; R: I where R R R and R are alkyl groups. Preferably the radicals Rand R are tertiary alkyl groups. In bothgroups of hindered phenols it ispreferable that none of the alkyl substituents contain more than fourcarbon atoms.

Phenols of these types have previously been suggested as anti-oxidantstabilizers for both natural and synthetic rubbers where they serve asprimary stabilizers to prevent deterioration of the rubber. For thispurpose, they are used in the customary amounts of 1 to 4% of therubber. On the other hand, the hindered phenolshave little or no primarystabilizing action in the customary amounts for viny chloride resins,the discoloration of vinyl chloride resins containing no otherstabilizer being about the same on heating, with or without the phenolsbeing present. Thus the hindered phenols of this invention are usefulsolely in combination with any of the known primary stabilizers forvinyl chloride resins where they exert a synergistic effect to increasethe over-all eflectivea ness of the combination. To exert thissynergistic efiect, only minute amounts of the phenols are required, theuseful range being 0.005 to 0.5% by weight of the vinyl chloride resins.

In order to show the synergistic effect of the 2,4,6, substitutedphenols on increasing the over-all stability of vinyl chloride resincompositions containing both the phenols and a primary stabilizer,comparative'heat sta' bility tests were made on compositions containingonly a primary stabilizer and only the phenols. The compositions testedwere as follows:

Com osition No.v I 7 Formula (parts by weight) p Polyvinyl chloride Theresults of the aging test in an air oven at 158 C. were:

Percentage Blue Light Reflectance after i Heating for- Composition N o.

0 Hr. 1.0 Er. 1.5 Hrs. 2.0 Hrs.

The results of these tests show that the phenols, by themselves, are noteffective as heat stabilizers. The color scale of the tests wasdetermined by the percentage reflectance of blue light on a scale inwhich 100, represents the reflectance of a white block of magnesium.carbonate. 1 a

'The formulas of the stabilized composition and controls were asfollows:

Polyvinyl chloride 100 parts.

Di(2-ethylhexyl)phthalate 40 parts.

Lead silicate 2 parts.

Stearic acid 0.5 part.

Titanium dioxide 1.0 part.

Phenolic compound 0.01 part (omitted from control).

The results of the tests were as follows:

Percentage Change Phenol Compound Reflectance Relative to l 7 afterMilling Control Control .(no phenol) l 77 Phenols Substituted other than2,4,6:

p=tertiary-amyl phenol 72 5 .p -isopropylphenol 67p-tertiary-amylphenol* 71 6 ,p-(alpha-phenethyl)phenol* 69 -82,4,6-Substituted Phenols: -2,4,fi tri-tert-butylphenol 83 +6G-dl-tert-butyl-4methyl-phenol 82 +5 2,2-rnethylenebis(4,6-dit e r t b ut y 1- phenol 80 +3 "*Dibutyl t'm dilaurate used as stabilizer in placeof lead silicate.

It is to be noted that only the 2,4,6-substituted phenols ofthisinvention reduced the color of the stabilized composition onmilling, whereas the other phenols caused an increase in color.

e auxiliary phenolic stabilizers of this invention may be used.in'combination with any primary stabilizer for vinyl chloride resin.'The more widely used of such primary stabilizersinclude the organo-tincompounds, such as dibutyl "tin dilaurate and dibutyl tin maleate; leadcompounds, such as lead carbonate, tribasic lead sulfate, litharge, leadsilicylate, lead maleate, dibasic lead phosphite, dibasic leadphthalate; alkali andalkaline metal salts, such as sodium carbonate,trimagnesium phosphate and calcium stearate; and epoxy compounds,suchias glycidyl oleate, the diglycidyl ethers of diphenols, and"glycidyl sorbate dimer. A primary stabilizer may be defined as anybase-reacting substance which absorbs substantially all of thehydrochloric acid formed 'by decomposition of the resin and'thus'prevents the catalytioetfect-of hydrochloric-acid on the various degradeti'oni'reactions. Furthermore, established tests are avail- 'of strongodors in stabilized plastic compositions.

by the blue'light reflectance method. Theresults o'fithe tests were asfollows:

Percentage Blue Light Reflectance After Oven Heating For- Phenol Added 70 Hr. 1.0, Hr. 1.5 Hrs. 2.0 Hrs.

None (control) 77 54 3S 2,4,6-tri-tert-bntyl phenol S3 78 69 592,6-di-tert-butyl-4- methyl phenoL 82 82 74 57 2,2-methylenebis(4,

6-ditert-butyl phenol) .l 77 70 60 In terms of visual observation, thesamples containing the phenols were light cream in color after heatingfor 1.5 hours, whereas the control sample was a deep, chocolate brown.

Example 2 -As previously mentioned, the 2,4,6-substituted phenols alsoact to prevent the development To illustrate this property, a basecomposition was prepared as a control having the following formula:

of this invention 7 Parts Copolymer of vinyl chloride and vinyl acetatevinyl chloride 400 Di(2-ethylhexyl)phthalate 324 Tribasic lead sulfate,PbSO -3PbO 23 Calcium'stearate 5.6 Stearic acid 3 able to determine theeffectiveness of any compound as a Example 1 Theftes't samplespreviously described containing the 2;4',6:substituted phenols" wereheated'for diiferent periods in an oven having access to the air andheated at 158" C. The color of the samples after heating was measuredSimilar compositions werealso prepared which contained in addition 0.4part respectively of 2,6-di-tertbutyl-4-methyl phenol and of2,2-methylenebis(4,6-ditertiarybutylphenol). Each composition was milledtor 15 minutes at C., and then removed from the mill as sheet 40 mils inthickness. .Each sheet was cut into thin strips and stored in a tightlyclosed gallon jar. After three days, the three jars were opened and itwas observed that the control sample had developed a strong, penetratingodor, While the samples containing the phenolsrhad only a mild odorwhich was very faint and unobjectionable in character.

The invention is not restricted to plastic 'composi tions containingdi(2-ethylhexyl)phthalate and is broadly useful in improving the colorand odor of vinyl chloride resins containing other plasticizers, such asmonomeric or polymeric esters of mono and difunctional acids andalcohols; esters of mono and difunctional acids and etheralcohols, suchas di(butoxyethyl)phthalate; epoxy compounds, such as glycidyl oleateand epoxidized soy bean oil; esters of alcohols and phosphoric acid,such as l cal decomposition and the development of color and odor onvheatingwhich comprises a vinyl chloride resin, a lead salt stabilizerfor the vinyl chloride resin, and an auxiliary stabilizer in an amountbetween 0.005 to 0.5% by weight of the vinyl chloride resin, said aux--iliary stabilizer being a 2,4,6-trialkyl substituted phenol in which theallcyl substituents in the 2,6-position are tertiary butyl radicals, andthe alkyl group in the 4-position contains up to four carbon atoms.

2. A plastic composition stabilized against both chemical decompositionand the development of color and odor on heating comprising polyvinylchloride, a lead silicate stabilizer and from"0.005 to 0.5% by weight ofthe polyvinyl chloride of 2,4,6-tri-tert-butylphenol.

3. A plastic composition stabilized against both chemisilicatestabilizer and from 0.005 to 0.5% by weight of cal decomposition and thedevelopment of color and the polyvinyl chloride of2,2'-metl1ylenebis(4,6-ditert odor on heating comprising polyvinylchloride, 21 lead butylphenol). silicate stabilizer and from 0.005 to0.5% by weight of the polyvinyl chloride of2,6-di-tert-butyl-4-methylphcnol. 5 References Cited in the file of thispatent 4. A plastic composition stabilized against both chemi- UNITEDSTATES PATENTS cal decomposition and the development of color and odoron heating comprising polyvinyl chloride, a lead 2564646 Lemme! et 1951

1. A PLASTIC COMPOSITION STABILIZED AGAINST BOTH CHEMICAL DECOMPOSITIONAND THE DEVELOPMENT OF COLOR AND ODOR OR HEATING WHICH COMPRISES A VINYLCHLORIDE RESIN, A LEAD SALT STABILIZER FOR THE VINYL CHLORIDE RESIN, ANDAN AUXILIARY STABILIZER IN AN AMOUNT BETWEEN 0.005 TO 0.5% BY WEIGHT OFTHE VINYL CHLORIDE RESIN, SAID AUXILIARY STABILIZER BEING SA2,4,6-TRIALKYL SUBSTITUTED PHENOL IN WHICH THE ALKYL SUBSTITUENTS IN THE2,6-POSITION ARE TERTIARY BUTYL RADICALS, AND THE ALKYL GROUP IN THE4-POSITION CONTAINS UP TO FOUR CARBON ATOMS.